Dehydrogenation of 2, 3-dimethyl-butane



March 23, 1948. F. E. FREY DEHYDROGENATION OF -2,5-DIHETHYLBUTANE FiledJan. 3, 1944 g-DIMETHYLBUTANE AND "2, DIMETHYLBUTENE 2 3 -DlMETHYL IBUTADlENE.-l,3

HYDROGEN AND 2,3-DIMETHYLBUTANE INVENTOR F. E. FREY BY M 9 ATTORNEFRACTIONATION ap-olma'r HYLsuTeNa-z Patented Mar. 23., 1948 UNITEDSTATES PATENT OFFICE DEHYDROGENATION OF 2,3-DIMETHYL- BUTANE FrederickE. Frey, Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation 01 Delaware Application January 3, 1944, Serial No. 516,799

This invention relates to the dehydrogenation of hydrocarbons. Moreparticularly, this invention relates to a process for the production ofolefins and diolefins by the dehydrogenation of more saturatedhydrocarbons containing the same number of carbon atoms per molecule andthe same carbon skeleton structure as the desired product. The processof this invention is particularly applicable to the production of 2,3dim'ethylbutadiene-1,3 by dehydrogenation of 2,3-di

come important in the processes of making synthetic rubbers as the artdevelops. v

The present invention is particularly concerned with the manufacture of2,3-dimethylbutadiene- 1,3. This conjugated dlolefln of the butadieneseries has been used as a monomer with 2-chlorobutadiene-1,3 to produceelastic polymers differing from the-polymers obtained from purechlorobutadiene.

The preparation of 2,3-dimethylbutadiene has been carried out by thereduction of acetone to pinacone anddehydration of the pinacone thusformedto 2,3-dlmethylbutadiene. It has been suggested that 2,3gdimethylbutadiene- 1,3 be made by the action of heated bases onpinacone chlorohydrin, and by dehydrochlorination of tetramethylethylenedichloride. By the process of the present invention2,3-dimethylbutadiene- 1,3 is made by a much more direct method, i. e.

by dehydrogenation of more saturated hydrocarbons containing the samenumber of carbon atoms per molecule and the same carbon skeletonstructure as 2,3-dimethylbutadiene-1,3.

This application is a continuation-in-part of 2 Claims. (01. 260-680)process to produce diolefln hydrocarbons by the dehydrogenation ofparafilns.

Still another object of this invention is to provide a process forconverting paraffins to diolefins in a single dehydrogenation step.

A further object of this invention is to provide an improved process forthe production of 2,3- dimethylbutadiene-1,3.

It is also an object of this invention to provide a process by which2,3-dimethylbutane may be converted to 2,3-dimethylbutadiene-1,3 bydehydrogenation under conditions which give good yields of2,3-dimethylbutadiene-1,3.

Other objects of this invention will be evident from the followingdetailed description of m process,

I have found that 2,3-dimethy1 bu-ta diene-1,3 may be producedbydehydrogen'a'tion of 2,3-dimethylbutane in the presence of suitablecatalysts. The dehydrogenation may be carried out in asingleflehydrogenation step. In the dehydrogenation of2,3-dimethylbutane in accordance ,-W1f;h my invention,2,3-dimethylbutene-1 and 2,3-

dimethylbutene-2 are formed, together with 2,3

dimethylbutadiene-l,3. The 2,3-dimethylbut enes' so formed may beconverted to 2,3-dimethylbutadiene by dehydrogenation under the sameconditions as 2,3-dimethylbutane is dehydrogenated. Thus, while thepresent invention is primarily concerned with the production of2,3-dimethyldimethylbutane and the production of2,3-dimethylbutadiene-LS from the 2,3-dimethylbutenes. I

The process is illustrated by the accompanying drawing which is a flowdiagram showing a suitable arrangement of apparatus for carrying out oneembodiment of the invention. The drawing is substantiallyself-explanatory. In the illustrated embodiment 2,3-dimethylbutane(diisopropyl) in substantially pure state is charged to thedehydrogenation step which comprises suitable heating units or furnaces,catalyst chambers, and the like known to the art for effecting catalyticdehydrogenation. The 2,3-dimethylbutane is heated to a temperaturewithin the range of about 1000 to 1100" F. and passed over thedehydrogenation catalyst comprising chromium oxide at relatively lowpressure. Preferably the dehydrogenation pressure is" subatmospheric;low pressure favors the dehydrogenation reaction.

Due to difliculties inherent in low pressure operations', it may bepreferable in some cases to operate at near-atmospheric or slightlyelevated pressure. A low partial pressure of the hydrocarbon materialpresent may be realized by admixing therewith a substantially inert gasas is known in the art.

T-hevtotal eilluent from the dehydrogenation is ,passed to afractionation means wherein hydrogen and any light hydrocarbons formedby the -scission of carbon-to-carbon bonds are removed jas overhead. ACc fractior'fcomposed of unrea cted aa-ufineth mutane,2,3-dirnethylbutenes,

fractionation means whereitis separated into Qtwo fractions. Thelower-boiling fraction com- ,/and 2,3-dimethylbutadiene is passed to asecond was passed for an hour over a chrome-alumina catalyst atatmospheric pressure, at an average temperature of 1097" F.," at a spacevelocity of 540 volumes of diisopropyl vapor per volume of catalyst perhour, and at a total space velocity of 2770 gas volumes per volume ofcatalyst per hour. The composition of the total eilluent was:

Fraction B. P., O. x g' C; and lighter hydrocarbons 22. 8 2,3-dimetylbutene-l 65. 62 1. 6 2,3-dimethylbutane 57. 99 63. 5

1 2,3-dimethylbutadiene-l,3 68. 9 8.0 2,3-dimothylbutene-2 73. 24 1. 8Deposit on catalyst- 2.4

Total- 100.0

.prising chiefly 2,3-dimethylbutane and 2,3-di-",

methylbutene-l is removed as an overhead fraction and is recycled to thedehydrogenation means. The higher-boiling fraction comprising chiefly2,3 dimethylbutene-2 and 2,3-dimethylbutadiene-1,3 is passed to a thirdfractionation means. The bottom product of the third fractionationcomprises chiefly 2,3 dimethylbutene-Z which isrecycled to thedehydrogenation to increase the yield of 2,3-dimethy-lbutadiene-1,3. Theoverhead product from the third fractionation comprising chiefly2,3-dimethylbutadiene-1,3 is withdrawn as the desired product of theproc-- ess. It will be evident to one skilled in the art that2,3-dimethylbutene-1 and 2,3-dime'thylbutene-2 are products of thedehydrogenation of 2,3-

dimethylbutane. If desired, one or more of the 2,3-dimethylbutenes maybe taken from the system as products; It will be evident also that 2,3-dimethylbutenes available from any other source may be fed into theprocess for conversion to 2,3-dimethylbutadiene-1,3 in accordancewith'niy' v invention.

Chromium oxide catalysts known to be generally efiective for catalyticdehydrogenation of petroleum hydrocarbons are suitable for use incatalyticmaterial is essentially an aluminum catalytically acoxidecarrier impregnated with tive chromium oxide.

Ereample V said 2,3-dimethylbutadiene-1,3 is recovered Number Name Date2,178,584 Grosse Nov. 7, 1939 2,209,215 .Wiezevlch et al. July 23, 19402,307,240 Ruthrufl Jan. 5, 1943 2,335,550 I Sturgeon-.. Nov. 30, 1943 7Pure diisopropyl (2,3-dimethylbutane) was 901-" at ilized'in a stream ofnitrogen and the mixture This result represents a conversion of 36.5 percent of the diisopropyl and a once-through yield of diolefln of 21.9 percent of the diisopropyl reacting. l

I- claim: I 1. A process for the production of 2,3-dlmethylbutadiene-1,3which comprises admixing 2,3-dimethylbutane with an inert diluent,passing the I resulting mixture into contact with a catalyst comprisingalumina impregnated with chromium oxide at substantially atmosphericpressure and at a temperature of about 1100" F. and a'space velocity ofabout 550 gas volumes of 2,3-dimethylbutane per volume of catalyst perhour and a total space velocity of about 2800 gas volumes per. volume ofcatalyst per hour effecting conversion of 2,3-dimethylbutane to2,3-dimethylbutene-l, 2,3-dlmethylbutene 2, and2,3-dimethylbutadiiene-'1 ,3.- v 2. The process of claim '1 in whichsaid inert diluent is nitrogen, said 2,3-dlmethylbutene-1 and2,3-dimethylbutene-2 are separated'from eilluents of said catalyst andare introduced into the mixture passed into contact with said catalyst,and as a product of the process.

- FREDERICK E. FREY.

9 REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED'STATE S PATENTS I

